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A new study, published in Oikos, shows that two major factors are important for goats survival — daylight hours and temperature — which get worse the further north you are.

The research used a catalogue of feral goat populations — made in the 1980s using NERC funding — to map where they lived. The team discovered that no populations could survive above 60 degrees latitude, unless farmers brought them in at night to protect them from the cold. North of this line temperatures in winter are too cold, food too sparse and days too short for goats to stay alive.

But warming global temperatures could make conditions bearable at these higher latitudes. The researchers looked at one specific population on the Isle of Rum, off the northwest coast of Scotland, to see how they were responding to climate in relation to day length.'As temperatures have started to climb by bits of a degree over the last half century we've been seeing the numbers of goats on the Isle of Rum increasing,' says Professor Robin Dunbar from the University of Oxford, who led the study.

Currently, the goats living on Rum barely have enough winter daylight hours to eat in. At these higher latitudes the goats struggle to keep warm. The colder it gets the more food they need to maintain their body temperature and the more time they spend feeding. But in colder weather the quality of vegetation deteriorates too, so a goat needs even more eating time to get enough energy to survive.

'The further north they go, the more the goats are trapped by a combination of the costs of thermoregulation and declining vegetation quality, both of which require them to spend more time feeding. But winter day lengths get shorter as you go further north. There comes a point where those two opposing forces crash together and they run out of time. That's the point north of which goats can't live,' explains Dunbar.